You cant quarantee 100% that the shot will be a perfect one, nobody can. 50yds is still a good poke and Deer are tough. I doubt that you'd get a complete pass through with 50grs at 50yds.
We owe it to the Animals that we Hunt that there Humanely Harvested. I dont know the Ballistics on a 50gr Load with your Sabot but you'll need at least 800ft lbs to do a good job on taking the Deer out. I know of no one who Hunts Deer with a 50gr Load. If your out there what's your story........